(function () {

    var C = (typeof window === 'undefined') ? require('./Crypto').Crypto : window.Crypto;

// Shortcuts
    var util = C.util,
        charenc = C.charenc,
        UTF8 = charenc.UTF8,
        Binary = charenc.Binary;

    C.HMAC = function (hasher, message, key, options) {

        // Convert to byte arrays
        if (message.constructor == String) message = UTF8.stringToBytes(message);
        if (key.constructor == String) key = UTF8.stringToBytes(key);
        /* else, assume byte arrays already */

        // Allow arbitrary length keys
        if (key.length > hasher._blocksize * 4)
            key = hasher(key, {asBytes: true});

        // XOR keys with pad constants
        var okey = key.slice(0),
            ikey = key.slice(0);
        for (var i = 0; i < hasher._blocksize * 4; i++) {
            okey[i] ^= 0x5C;
            ikey[i] ^= 0x36;
        }

        var hmacbytes = hasher(okey.concat(hasher(ikey.concat(message), {asBytes: true})), {asBytes: true});

        return options && options.asBytes ? hmacbytes :
            options && options.asString ? Binary.bytesToString(hmacbytes) :
                util.bytesToHex(hmacbytes);

    };

})();
